The present disclosure relates to a method for manufacturing an oriented film in which latent images are stored while being overlaid on one another and to a method for manufacturing a display body that is provided with an oriented film.
Negotiable securities such as bank notes and gift certificates, and authenticated media such as passports have a display body, which is hard to counterfeit, in order to prevent a counterfeit thereof. Such a display body is used for the determination of authenticity by visual determination or by determination using a verification device. A display body of which the authenticity can be visually determined is easy to be counterfeited by another person. For this reason, in recent years, a display body is proposed that stores a latent image therein that is formed with the use of a polarization technology. The latent image stored in this display body appears when a filter, which is the verification device, is overlaid thereon.
For instance, Japanese Laid-Open Patent Publication No. 2009-258151 proposes a display body that stores latent images therein in such a state that the latent images are overlaid on each other. The display body stores two latent images that are overlaid on each other, by four regions having different orientation properties from each other.
An optical orientation method is known as a method for giving a plurality of different orientation properties from each other, to an oriented film with which the display body is provided. In the optical orientation method, a photosensitive film, which functions as the oriented film, is irradiated with polarized light, while four photomasks corresponding to the respective orientation directions are switched. In such a method, the positions of the photomasks need to be aligned with each other. When the four photomasks are switched, the positions of the photomasks with respect to the photosensitive film must be aligned with a precision of such a degree that these regions are precisely divided, the alignment of the photomasks is naturally difficult.
On the other hand, in a method of using one phase-difference filter, a photosensitive film needs only one-time irradiation with polarized light, but patterns corresponding to the above described four regions need to be formed in the one phase-difference filter. For this reason, a process of forming the phase difference filter is complicated, and as a result, a long time results in being spent on the manufacture of the phase difference filter. In addition, also when two phase-difference filters are used, it is difficult to align the positions of each of the phase difference filters with respect to the photosensitive film, similarly to the above described method using the photomask.